168 
IOWA ACADEMY OF SCIENCES 
(1) . Wolcott Gibbs conducted a series of experiments by which he 
concluded that it is more convenient to precipitate magnesium from a 
boiling concentrated solution with microcosmic salt instead of in the cold 
with disodium phosphate. The mean of four determinations with pure 
crystalized magnesium sulphate was .06 2-3 per cent, too high in MgO. 
While by the addition of ammonium chloride, it was reduced to .03 1-3 
per cent, too high. Two analyses were next made by precipitating the 
boiling solution of disodium phosphate, after the addition of ammonium 
chloride. The result was .58 per cent, too high in MgO. When the pre- 
cipitate thus obtained was dissolved in hydrochloric acid and re-pre- 
cipitated with ammonia, the result was only .05 per cent, too high in MgO. 
(2) . Gooch and Austin conducted a valuable series of experiments, 
the object of which was to determine when results too high in magnesium 
are obtained, whether such results are due to mechanical occlusion in 
the crystalline phosphate, or to a variation in the magnesium ammonium 
phosphate, obtaining a product richer in ammonia and poorer in magnes- 
ium. They used microcosmic salt as the precipitant and obtained a salt 
(NH 4 ) 4 Mg(P 04 )a to a greater or less extent with the ideal magnesium 
ammonium phosphate, MgNH 4 P 04 , which would give a result too high 
in magnesium. To obtain the ideal salt, the first precipitate must be 
dissolved in hydrochloric acid and re-precipitated with ammonia. The 
authors commend the method of Gibbs of using microcosmic salt as the 
precipitant, and claim that by boiling the solution from three to five min- 
utes the ideal salt is readily obtained. 
We have repeated the separation of calcium and magnesium by the 
method described on page 127 of the Proceedings of the Iowa Academy of 
Sciences of the Year 1903, and still commend its accuracy and simplicity. 
The solution of ammonium oxalate was prepared by dissolving 10 grams 
of the purest obtainable crystals in 275cc of distilled water. The amount 
in a cubic centimetre was thus easily known. To insure the greatest 
possible accuracy, the precipitant should not be taken from a stock solu- 
tion, but should be made up as required, on account of the solvent action 
upon glass. The solutions of calcium and magnesium chlorides were 
heated to boiling and kept at that temperature while the theoretical 
amount of the ammonium oxalate solution necessary to precipitate the 
calcium was added, and then two to four centimetres additional. After 
standing at least eight hours, the precipitate was filtered off. The filtrate 
was tested with one or two centimetres of the ammonium oxalate solu- 
tion to learn if all the calcium was precipitated which was usually found 
to be the case. We thus learned that it did not seem necessary to add 
sufficient ammonium oxalate to change all the magnesium chloride into 
oxalate on account of the supposed solubility of calcium oxalate in mag- 
nesium chloride. It is doubtless true that in precipitating magnesium an 
excess of ammonium exalate does no harm, contrary to the teaching 
of some of the text-books, but an excess of ammonium salts simply re- 
tards the precipitation of magnesium. It is therefore unnecessary to 
remove the ammonium salts by heat before precipitating the magnesium. 
1. Am. J. Science 3. 5. 114. 1873. 
2. American J. Science 4. 7. 187. 1899. 
